The official estimate of the number of HIV positive people in India is 3.5 million. This figure places India as the country with the second largest number of HIV infections in the world, behind South Africa. However, unofficial estimates of HIV infection in India place India as the country with the highest number of infections in the world.

The nature and scale of the HIV epidemic varies within different parts of India. Injecting drug use plays, an important role in various local epidemics, even though most infections in India are through sexual transmission. HIV spreads very quickly through populations of injecting drug users, this has rapidly created substantial populations of people in various places who are HIV positive and are sexually active in the broader society, thereby both stimulating new epidemics (such as in Manipur and Bihar) and fuelling existing epidemics (e.g. Chennai).